Cryogenic rectification process-based method for producing air product, and air separation system

ABSTRACT

The present invention discloses a cryogenic rectification process-based method for producing an air product, and an air separation system. By adding an air product outlet line and a liquid air booster pump to an existing cryogenic rectification process apparatus, the existing rectification apparatus is used to prepare oxygen-enriched liquid air by pressurizing, cooling and liquefying feed air; and moreover, a high-pressure or ultra-high-pressure air product can be prepared according to customer requirements by adjusting the ratio of the feed air to the oxygen-enriched liquid air, and pressurizing the mixture to a target pressure by the liquid air booster pump before being vaporized via heat exchange with a gas or liquid product produced by rectification through a heat exchange apparatus. According to the present invention, when gas or liquid products of oxygen and nitrogen are produced by means of rectification, a high-pressure or ultra-high-pressure air product can be provided according to customer requirements, and there is no need to provide an additional air compressor or passively increase the discharge pressure of the air booster, so that the production costs are greatly reduced and the energy efficiency level is improved. The method of the present invention can also improve the stability of devices, especially when a small amount of high-pressure/ultra-high-pressure air product needs to be produced.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/CN2017/119240, filed Dec. 28, 2017, which is herein incorporated by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention belongs to the field of air separation and relates to an air separation process, in particular to a cryogenic rectification process-based method for producing an air product, and an air separation system.

BACKGROUND OF THE INVENTION

Cryogenic rectification is essentially a technology for gas liquefaction, in which mechanical methods, such as throttling expansion or adiabatic expansion, are usually used to compress and cool gases, and then rectify the gases by taking advantage of the difference in boiling points of different gases to separate the different gases. Specifically, air is taken as a feedstock and liquefied after being subject to compression, purification and heat exchange, and nitrogen and oxygen are obtained after separation through rectification by taking advantage of different boiling points of liquid oxygen and liquid nitrogen.

Using cryogenic rectification to separate air into nitrogen and oxygen products is a common and sophisticated technology. At least two air separation columns (a medium-pressure column and a low-pressure column) operating at different pressures communicate with each other in a heat exchange manner through a main condenser/evaporator. Pressurized, purified and cooled feed air is fed into the medium-pressure column and/or the low-pressure column, and gaseous and/or liquid nitrogen and oxygen products are obtained through rectification. All or part of the nitrogen and oxygen exchange heat with the feed air in a main heat exchanger to obtain gaseous nitrogen and oxygen products at a normal atmospheric temperature. The design of the air separation system and process is generally based on customer requirements on the state, pressure and output scale of the nitrogen and oxygen products. To produce an oxygen and/or nitrogen product with a high pressure, e.g., greater than 40 bara, there may be two modes to choose from, i.e., an external pressurization mode in which gaseous oxygen or nitrogen that has been reheated to the normal atmospheric temperature through the main heat exchanger is passed through a corresponding booster for pressurization, or an internal pressurization mode in which liquid oxygen or liquid nitrogen at a low temperature is boosted to a required pressure using a pump before being reheated by the main heat exchanger.

In coal chemical projects, the internal compression process is widely used in modern air separation. To produce a medium-pressure or high-pressure air product, an air booster is usually provided, through which the required medium-pressure or high-pressure air product can be produced. However, to produce an air product with a pressure higher than a discharge pressure of the air booster itself, it is no longer viable to rely solely on this air booster, and it is usually necessary to provide an additional high-pressure/ultra-high-pressure compressor or passively increase the discharge pressure of the air booster. However, all these methods will compromise the overall energy consumption level of the air separation device.

SUMMARY OF THE INVENTION

The purpose of certain embodiments of the present invention is to avoid being forced to set up an additional air compressor or passively increasing the discharge pressure of the air booster. By utilizing an existing cryogenic rectification process apparatus, pressurized and at least partially liquefied feed air and/or oxygen-enriched liquid air is passed through a liquid air booster pump for pressurization to a required high pressure or ultra-high pressure, and then a high-pressure or ultra-high-pressure air product is discharged along an air product outlet line after vaporization via heat exchange through a heat exchange apparatus. The present invention can not only improve the energy efficiency, but also reduce the costs and improve the stability of the device. The air product can be air, air mixed with oxygen-enriched liquid air, or oxygen-enriched liquid air.

In order to achieve the above object, the present invention provides a cryogenic rectification process-based method for producing an air product, comprising:

(a) providing an air separation system for preparing a nitrogen product and/or an oxygen product, which comprises: a rectification column, at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus and at least one heat exchange apparatus, wherein the rectification column comprises a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and the air boost system comprises a main air compressor and at least one air booster;

(b) after passing feed air sequentially through the main air compressor for pressurization to a first pressure range, the air pre-cooling apparatus for pre-cooling and the air purification apparatus for purification, splitting off one portion thereof as a first air stream for heat exchange through the heat exchange apparatus with a gas or liquid product produced by rectification, and then introducing the first air stream after cooling down into the first column for rectification; and the other portion passing through the air booster for pressurization to a third pressure range before being split into a second air stream and a third air stream, the second air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification and being discharged from a middle part of the heat exchange apparatus into an air expander for depressurization to the first pressure range before being introduced into the first column for rectification; and the third air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, being depressurized to the first pressure range for introduction into the first column or depressurized to a second pressure range for introduction into the second column; and

(c) providing a liquid nitrogen line and an oxygen-enriched liquid air line which introduce liquid nitrogen at the top of the first column and oxygen-enriched liquid air at the bottom of the first column, respectively, into the second column as reflux for rectification;

the method further comprising: providing an air product outlet line in which at least one liquid air booster pump is arranged, and discharging the oxygen-enriched liquid air or at least partially liquefied feed air of the third air stream from the bottom of the first column through the air product outlet line, into the liquid air booster pump for pressurization to a target pressure, and then into the heat exchange apparatus for vaporization via heat exchange so as to obtain the required air product.

Preferably, the air expander uses an expander booster for braking, the third air stream is first pressurized to a fourth pressure range by the expander booster, then enters the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, is depressurized to a first pressure range by a pressure reducing apparatus and then introduced into the first column.

Preferably, the pressure reducing apparatus is a throttle valve or a liquid expander.

Preferably, the liquid expander is braked by a generator.

Preferably, a fourth air stream is further split off from the third air stream that has been depressurized to the first pressure range, and the fourth air stream is introduced into the second column after being throttled and depressurized to the second pressure range by a throttle valve.

Preferably, a fifth air stream is further split off from the fourth air stream, the fifth air stream is connected to the air product outlet line, and the flow rate and flow velocity of the fifth air stream are controlled via a first regulating valve.

Preferably, the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air.

Preferably, the heat exchange apparatus comprises a low-pressure plate heat exchanger and a high-pressure plate heat exchanger, or an integral combined heat exchanger.

Preferably, the heat exchange apparatus further comprises a subcooler through which the reflux entering the second column exchanges heat with the gas or liquid product rectified by the second column.

Preferably, the method further comprises: drawing a liquid nitrogen fraction from the first column into the second column as reflux.

Preferably, the method further comprises: drawing liquid oxygen from the main condensation and evaporation apparatus through a liquid oxygen booster pump for pressurization to a required pressure and then into the heat exchange apparatus for heat exchange and vaporization for preparation of the oxygen product.

Preferably, the method further comprises: drawing the liquid nitrogen from the top of the first column directly into the heat exchange apparatus for vaporization via heat exchange for preparation of a first nitrogen product; or, drawing the liquid nitrogen from the top of the first column through a liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product.

Preferably, the method further comprises: drawing ultra-low-pressure nitrogen from the top of the second column into the heat exchange apparatus for reheating to prepare a third nitrogen product.

Preferably, the method further comprises: drawing waste nitrogen from an upper part of the second column into the heat exchange apparatus for reheating to obtain a waste nitrogen product.

The present invention also provides an air separation system for producing an air product based on a cryogenic rectification process, the air separation system comprising:

(a) a rectification column, which comprises: a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and a liquid nitrogen line for guiding liquid nitrogen from the top of the first column through a throttle valve into the second column and an oxygen-enriched liquid air line for guiding oxygen-enriched liquid air from the bottom of the first column through the throttle valve into the second column arranged between the first column and the second column;

(b) at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus, at least one heat exchange apparatus, at least one air expander, at least one liquid oxygen booster pump, at least one liquid air booster pump and a plurality of pressure reducing apparatuses, the air boost system comprising a main air compressor and at least one air booster;

(c) a first air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus, the air purification apparatus and the heat exchange apparatus into the first column; a second air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus and the air purification apparatus, out of the heat exchange apparatus and then through the air expander into the first column; and a third air inlet line further branching off from the second air inlet line before the second air inlet line enters the heat exchange apparatus, the third air inlet line passing through the heat exchange apparatus directly and being connected to the first column or the second column via the pressure reducing apparatus; and

(d) a liquid oxygen product outlet line for discharging liquid oxygen from the main condensation and evaporation apparatus through the at least one liquid oxygen booster pump and then through the heat exchange apparatus;

and further comprising: an air product outlet line connected to the bottom of the first column or the third air inlet line, the air product outlet line being provided with the at least one liquid air booster pump to pressurize at least partially liquefied feed air from the third air inlet line or the oxygen-enriched liquid air discharged from the bottom of the first column to a target pressure for vaporization via heat exchange through the heat exchange apparatus so as to output the required air product.

Preferably, the air expander is braked by an expander booster provided, and the third air inlet line is connected via the expander booster and subsequently the heat exchange apparatus and the pressure reducing apparatus to the first column.

Preferably, the system further comprises a fourth air inlet line, which branches off from the third air inlet line connecting the pressure reducing apparatus to the first column and is connected to the second column via the throttle valve.

Preferably, a fifth air inlet line further branches off from the fourth air inlet line, the fifth air inlet line being connected to the air product outlet line for outputting a high-pressure or ultra-high-pressure air product discharged through the liquid air booster pump and the heat exchange apparatus.

Preferably, the fifth air inlet line is further provided with a first regulating valve for controlling the flow rate and flow velocity of an air stream; and the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air.

Preferably, the system further comprises: a first nitrogen product outlet line for vaporizing the liquid nitrogen from the top of the first column via heat exchange through the heat exchange apparatus for preparation of a first nitrogen product; or, at least one liquid nitrogen booster pump, and a second nitrogen product outlet line passing the liquid nitrogen drawn from the top of the first column through the at least one liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product; or, a third nitrogen product outlet line discharging nitrogen from the top of the second column through the heat exchange apparatus.

Preferably, a liquid nitrogen fraction line for guiding a liquid nitrogen fraction from the first column through the throttle valve into the second column is further arranged between the first column and the second column.

Preferably, the system further comprises a waste nitrogen line for discharging waste nitrogen from the second column through the heat exchange apparatus.

The method provided by the present invention for producing a high-pressure or ultra-high-pressure air product uses the existing cryogenic rectification process apparatus. According to customer requirements, the oxygen-enriched liquid air produced by rectification from the rectification column, or the feed air that is pressurized and cooled so as to be at least partially liquefied, or the oxygen-enriched liquid air mixed with the at least partially liquefied feed air at an required ratio is passed through a liquid air booster pump for pressurization to a required high pressure or ultra-high pressure, and then a high-pressure or ultra-high-pressure air product is discharged along an air product outlet line after vaporization via heat exchange through a heat exchange apparatus. According to the present invention, there is no need to provide an additional air compressor or passively increase the discharge pressure of the air booster, so that the production costs are greatly reduced and the energy efficiency level is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, advantages and possible applications of the invention are apparent from the following description of working and numerical examples and from the drawings. All described and/or depicted features on their own or in any desired combination form the subject matter of the invention, irrespective of the way in which they are combined in the claims or the way in which said claims refer back to one another.

FIG. 1 is a schematic structural diagram of an air separation system for producing an air product based on a cryogenic rectification process of the present invention, with an air product outlet line 113 connected to both a fifth air inlet line 105 and an oxygen-enriched liquid air bottom.

FIG. 2 is a schematic structural diagram of another air separation system for producing an air product based on a cryogenic rectification process of the present invention, with the air product outlet line 113 connected to the fifth air inlet line 105 only.

DETAILED DESCRIPTION OF THE INVENTION

The technical solution of the present invention is explained further below in conjunction with the accompanying drawings and embodiments.

In the present invention, the term “feed air” refers to a mixture mainly containing oxygen and nitrogen.

The term “waste nitrogen” refers to a gaseous fluid with a nitrogen purity generally no less than 95%; and the term “liquid nitrogen fraction” refers to a liquid fluid with a nitrogen purity generally greater than 95%, all of which are expressed in mole percent.

The term “oxygen-enriched liquid air” refers to a liquid fluid with an oxygen purity greater than 30%; the term “liquid air” refers to a liquid fluid with an oxygen purity no greater than 30%; and the term “liquid oxygen” refers to a liquid fluid with an oxygen purity greater than 99%, the oxygen purity of the “liquid oxygen” being higher than that of the “oxygen-enriched liquid air”, all of which are expressed in mole percent.

The pressure range indicated by the term “medium pressure” is 5-30 bara, the pressure range indicated by the term “high pressure” is 30-80 bara, and the pressure range indicated by the term “ultra-high pressure” is over 80 bara.

In the present invention, the “first pressure range” is consistent with the working pressure range of the first column (medium-pressure column), which is generally 5-6.5 bara, and the feed air at a normal atmospheric pressure can be compressed by the main air compressor to reach this pressure range. The “second pressure range” is consistent with the working pressure range of the second column (low-pressure column), which is generally 1.1-1.5 bara. The “third pressure range” is a pressure range that the feed air in the first pressure range reaches after being pressurized by an air booster, which is generally 40-60 bara. The “fourth pressure range” is a pressure range the feed air in the third pressure range reaches after being further pressurized by an expander booster, which is generally 60-75 bara. The feed air in the third and fourth pressure ranges needs to be able to exchange heat with and thus vaporize the pressurized liquid oxygen in the heat exchange apparatus, so its specific pressure is determined by the pressure of the liquid oxygen to be vaporized.

The cryogenic rectification of the present invention is a rectification method at least partially carried out at a temperature of 150 K or lower than 150 K. As used herein, the term “column” means a distillation or fractionating column or zone in which liquid and gas phases are in countercurrent contact to effectively separate the fluid mixture. In the present invention, the operating pressure of the “first column” is generally 5-6.5 bara, which is higher than the general operating pressure of the “second column” of 1.1-1.5 bara. The second column can be installed vertically on top of the first column or the two columns can be installed side by side. The “first column” is also commonly referred to as a medium-pressure column or a lower column, and the “second column” is also commonly referred to as a low-pressure column or an upper column. The main condensation and evaporation apparatus is generally located at the bottom of the “second column”, which can produce pure liquid nitrogen at the top of the first column after condensing the pure nitrogen gas produced at the top of the first column via heat exchange with the pure liquid oxygen produced at the bottom of the second column, and evaporate the pure liquid oxygen partially at the same time. The types of main condensation and evaporation apparatus include a shell-and-tube type, a falling film type, an immersion type, etc. In the present invention, an immersion type condenser/evaporator can be used.

An air pre-cooling apparatus in the present invention is used to pre-cool high temperature air (70-120° C.) discharged from the main air compressor to a temperature suitable for entering an air purification apparatus (generally at 10-25° C.). High-temperature air generally exchanges heat by contact with common circulating cooling water and low-temperature water (generally at 5-20° C.) in an air cooling column to achieve the purpose of cooling. The low-temperature water can be obtained with the ordinary circulating cooling water via heat exchange by contact with a gas product or by-product, such as the waste nitrogen, produced by the air separation apparatus, or by means of a refrigerator.

The air purification apparatus refers to a purification device that removes dust, water vapor, CO₂, hydrocarbons, etc. from the air. In the present invention, a pressure swing adsorption method is generally used, in which an adsorbent involved may optionally be a molecular sieve plus alumina, or a molecular sieve only.

In the main heat exchanger, the compressed, pre-cooled and purified feed air is subject to non-contact heat exchange with the gas and/or liquid product produced by rectification and is cooled to a temperature close to or equal to the rectification temperature of the first column, generally lower than 150 K. Common main heat exchangers include split or integrated types, etc. The main heat exchangers are divided into high-pressure (>20 bara pressure) and low-pressure (<20 bara pressure) heat exchangers according to proper pressure ranges. The present invention can use both a high-pressure plate heat exchanger and a low-pressure plate heat exchanger, or an integral combined heat exchanger.

The present invention provides an air separation system for producing an air product based on a cryogenic rectification process, which is an air separation system for producing a high-pressure or ultra-high-pressure air product by adding an air product outlet line and at least one liquid air booster pump to an existing cryogenic rectification process device.

As shown in FIG. 1, an air separation system for producing an air product based on a cryogenic rectification process of the present invention comprises:

(a) a rectification column, which comprises: a first column 11 (a medium-pressure column) with a first pressure, a second column 12 (a low-pressure column) with a second pressure and a main condensation and evaporation apparatus 13 arranged at the bottom of the second column 12; and a liquid nitrogen line 111 for guiding liquid nitrogen from the top of the first column 11 through a throttle valve 14 into the second column 12 and an oxygen-enriched liquid air line 112 for guiding oxygen-enriched liquid air from the bottom of the first column 11 through the throttle valve 14 into the second column 12 arranged between the first column 11 and the second column 12;

(b) at least one air boost system, at least one air pre-cooling apparatus 40, at least one air purification apparatus 50, at least one heat exchange apparatus, at least one air expander 1021, at least one liquid oxygen booster pump 1311, at least one liquid air booster pump 1131 and a plurality of pressure reducing apparatuses, the air boost system comprising a main air compressor 21 and at least one air booster 22;

(c) a first air inlet line 101 for guiding feed air through the main air compressor 21, the air pre-cooling apparatus 40, the air purification apparatus 50 and the heat exchange apparatus into the first column 11; a second air inlet line 102 for guiding feed air through the main air compressor 21, the air pre-cooling apparatus 40, the air purification apparatus 50 and the heat exchange apparatus, and discharging same from a middle part of the heat exchange apparatus (the middle part is not limited to the very center of the heat exchange apparatus, and instead refers to the incompletely liquefied air being discharged before completely passing through the heat exchange apparatus) and then through the air expander 1021 (which is braked by an expander booster 1031 provided) into the first column 11; and a third air inlet line 103 further branching off from the second air inlet line 102 before the second air inlet line enters the heat exchange apparatus, the third air inlet line 103 being connected to the first column 11 via the expander booster 1031 and then via the heat exchange apparatus and the pressure reducing apparatus;

(d) a liquid oxygen product outlet line 131 for discharging liquid oxygen from the main condensation and evaporation apparatus 13 through the at least one liquid oxygen booster pump 1311 and then through the heat exchange apparatus; and

(e) an air product outlet line 113 connected to the bottom of the first column 11 or the third air inlet line 103, wherein the air product outlet line 113 is provided with the at least one liquid air booster pump 1131, and oxygen-enriched liquid air discharged from the bottom of the first column 11 and/or at least partially liquefied feed air discharged from the third air inlet line 103 is pressurized to a target pressure via the at least one liquid air booster pump 1131 for vaporization via heat exchange through the heat exchange apparatus so as to output the required high-pressure or ultra-high-pressure air product, which can be the oxygen-enriched liquid air, the feed air, or a mixture of the oxygen-enriched liquid air and the feed air.

In some embodiments, a fourth air inlet line 104 further branches off from the third air inlet line 103 between the pressure reducing apparatus and the first column 11 and is connected to the second column 12 via the throttle valve 14 for directly feeding the liquefied feed air into the second column 12.

In some embodiments, a fifth air inlet line 105 further branches off from the fourth air inlet line 104 and is connected to the air product outlet line 113 for guiding the at least partially liquefied feed air discharged from the third air inlet line 103 into the air product outlet line 113 to be mixed with oxygen-enriched liquid air, and the mixture is pressurized to a target pressure via the at least one liquid air booster pump 1131 for vaporization via heat exchange through the heat exchange apparatus so as to output the required high-pressure or ultra-high-pressure air product, which is a mixture of the oxygen-enriched liquid air and the feed air.

In some embodiments, the fifth air inlet line 105 is further provided with a first regulating valve 1051, which is used to control the flow rate and flow velocity of the air stream and can control the mixing ratio of the feed air to the oxygen-enriched liquid air so as to obtain the air product with the required oxygen ratio. The first regulating valve 1051 can also be closed on demand in order that the air product outlet line 113 only outputs oxygen-enriched liquid air.

In some embodiments, the air product outlet line 113 is further provided with a second regulating valve 1132, which is used to control the flow rate and flow velocity of the oxygen-enriched liquid air and can control the mixing ratio of the feed air to the oxygen-enriched liquid air so as to obtain the air product with the required oxygen ratio. The second regulating valve 1132 can also be closed on demand in order that the air product outlet line 113 only outputs high-pressure or ultra-high-pressure feed air.

In some embodiments, the fifth air inlet line 105 is provided with the first regulating valve 1051, and the air product outlet line 113 is further provided with the second regulating valve 1132, so as to accurately adjust the oxygen ratio in the air product to meet different requirements of customers.

In some embodiments, the air separation system further comprises: a first nitrogen product outlet line 115 for vaporizing the liquid nitrogen from the top of the first column 11 via heat exchange through the heat exchange apparatus for preparation of a first nitrogen product.

In some embodiments, the air separation system further comprises: at least one liquid nitrogen booster pump 1161, and a second nitrogen product outlet line 116 passing the liquid nitrogen drawn from the top of the first column 11 through the at least one liquid nitrogen booster pump 1161 first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product.

In some embodiments, the air separation system further comprises a third nitrogen product outlet line 121 discharging nitrogen from the top of the second column 12 through the heat exchange apparatus.

In some embodiments, the air separation system further comprises: a waste nitrogen line 122 for discharging waste nitrogen from the second column 12 through the heat exchange apparatus.

In some embodiments, a liquid nitrogen fraction line 114 for guiding a liquid nitrogen fraction from the first column 11 through the throttle valve 14 into the second column 12 is further provided between the first column 11 and the second column 12.

In some embodiments, the heat exchange apparatus comprises a low-pressure plate heat exchanger 31 and a high-pressure plate heat exchanger 32 as the main heat exchanger.

In some embodiments, the heat exchange apparatus uses an integral combined heat exchanger as the main heat exchanger.

In some embodiments, the heat exchange apparatus further comprises a subcooler 33 for the reflux entering the second column 12 to exchange heat with the gas or liquid product rectified by the second column 12.

In some embodiments, a throttle valve or a liquid expander 1032 is selected as the pressure reducing apparatus.

In some embodiments, the air expander 1021 in the second air inlet line 102 is braked by a generator. A third air inlet line 103 further branches off from the second air inlet line 102 before the second air inlet line enters the heat exchange apparatus, the third air inlet line 103 passing through the heat exchange apparatus directly and completely and being connected to the first column 11 or the second column 12 via the pressure reducing apparatus.

In some embodiments, the air product outlet line 113 is only connected to the third air inlet line 103 (not connected to the bottom of the first column 11), the air product outlet line 113 is provided with the at least one liquid air booster pump 1131, and at least partially liquefied feed air discharged from the third air inlet line 103 is pressurized to a target pressure via the at least one liquid air booster pump 1131 for vaporization via heat exchange through the heat exchange apparatus so as to output the required high-pressure or ultra-high-pressure air product, which is high-pressure or ultra-high-pressure feed air.

In some embodiments, as shown in FIG. 2, the air product outlet line 113 is only connected to the fifth air inlet line 105, and is not connected to the bottom of the first column 11, i.e., does not discharge the oxygen-enriched liquid air. The air product outlet line 113 is provided with the at least one liquid air booster pump 1131, and at least partially liquefied feed air discharged from the fifth air inlet line 105 is pressurized to a target pressure via the at least one liquid air booster pump 1131 for vaporization via heat exchange through the heat exchange apparatus so as to output the required high-pressure or ultra-high-pressure air product, which is high-pressure or ultra-high-pressure feed air.

In some embodiments, the fifth air inlet line 105 is further provided with the first regulating valve 1051 to control the flow rate and flow velocity of the feed air.

The method for producing a high-pressure or ultra-high-pressure air product by using the air separation system of the present invention will be described in detail below with reference to embodiments.

Embodiment 1

After feed air (1 bara) sequentially passes through the main air compressor 21 for pressurization to 6 bara (the first pressure range), the air pre-cooling apparatus 40 for pre-cooling and the air purification apparatus 50 for purification, one portion thereof is split off as a first air stream guided along the first air inlet line 101, through the heat exchange apparatus (the low-pressure plate heat exchanger 31) for heat exchange with a gas or liquid product produced by rectification (e.g., liquid nitrogen discharged from the top of the first column, and/or liquid nitrogen discharged from the top of the second column, and/or a liquid nitrogen fraction discharged from an upper part of the second column), and after cooling down (6 bara), into the first column 11 for rectification; and the other portion passes through the air booster 22 for pressurization to 50 bara (the third pressure range) before being split into a second air stream and a third air stream: the second air stream is guided along the second air inlet line 102 through the heat exchange apparatus (the high-pressure plate heat exchanger 32) for heat exchange with the gas or liquid product produced by rectification (e.g., liquid oxygen from the main condensation and evaporation apparatus, and/or liquid nitrogen from the top of the first column, and/or the high-pressure or ultra-high-pressure air product from the air product outlet line) and is discharged from a middle part of the heat exchange apparatus (the high-pressure plate heat exchanger 32) into the air expander 1021 for depressurization to 6 bara (the first pressure range) before being introduced into the first column 11 for rectification; and the third air stream is guided along the third air inlet line 103, first pressurized to 70 bara (the fourth pressure range) by the expander booster 1031, then enters the heat exchange apparatus (the high-pressure plate heat exchanger 32) for heat exchange with the gas or liquid product produced by rectification, and after cooling down, is depressurized to 6 bara (the first pressure range) by the pressure reducing apparatus (the liquid expander 1032) and then introduced into the first column 11.

A fourth air stream is further split off from the third air stream that has been depressurized to the first pressure range, and the fourth air stream is guided along the fourth air inlet line 104, and introduced into the second column 12 as reflux after being first cooled to subcooled liquid air by the subcooler 33 and then throttled and depressurized to 1.2 bara (the second pressure range) by the throttle valve 14.

A fifth air stream is further split off from the fourth air stream, the fifth air stream is connected to the air product outlet line 113, and the flow rate and flow velocity of the fifth air stream are controlled via a first regulating valve 1132.

The oxygen-enriched liquid air discharged from the bottom of the first column and the fifth air stream are mixed in the air product outlet line 113. The ratio of the oxygen-enriched liquid air to the feed air is adjusted by the first regulating valve 1051 and the second regulating valve 1132 so as to accurately adjust the oxygen ratio in the air product. The mixture is further pressurized to 80 bara via the liquid air booster pump 1131 for subsequent vaporization via heat exchange through the heat exchange apparatus (the high-pressure plate heat exchanger 32) so as to obtain the required high-pressure or ultra-high-pressure air product (80-bara air product), to meet different customer requirements.

In some embodiments, in the rectification column, the liquid nitrogen (5.5 bara LIN) at the top of the first column 11 is discharged through the liquid nitrogen line 111, cooled by the subcooler 33, and depressurized to 1.1 bara via the throttle valve 14 and then introduced into the second column 12 as reflux for rectification.

In some embodiments, in the rectification column, the oxygen-enriched liquid air (6 bara) at the bottom of the first column 11 is discharged through the oxygen-enriched liquid air line 112, cooled by the subcooler 33, and depressurized to 1.3 bara via the throttle valve 14 and then introduced into the second column 12 as reflux for rectification.

In some embodiments, in the rectification column, the liquid nitrogen fraction (5.8 bara) is drawn from the first column 11 through the liquid nitrogen fraction line 114, depressurized to 1.1 bara via the throttle valve 14, and then introduced into the second column 12 as reflux for rectification.

In some embodiments, liquid oxygen (2 bara) is drawn from the main condensation and evaporation apparatus 13, along the liquid oxygen product outlet line 131, pressurized to a required pressure (e.g., 80 bara) through the liquid oxygen booster pump 1311, and then vaporized via heat exchange through the heat exchange apparatus (the high-pressure plate heat exchanger 32) for preparation of a high-pressure oxygen product of 80 bara.

In some embodiments, liquid nitrogen (5.5 bara) is drawn from the top of the first column 11, along the first nitrogen product outlet line 115, directly vaporized via heat exchange through the heat exchange apparatus (the low-pressure plate heat exchanger 31) for preparation of a low-pressure and high-purity nitrogen of 5 bara (the first nitrogen product).

In some embodiments, liquid nitrogen (5.5 bara) is drawn from the top of the first column 11, along the second liquid nitrogen product outlet line 116, first pressurized to a required pressure (e.g., 50 bara) through the liquid nitrogen booster pump 1161, and then vaporized via heat exchange through the heat exchange apparatus (the high-pressure plate heat exchanger 32) for preparation of a second nitrogen product of 50 bara.

In some embodiments, ultra-low-pressure nitrogen (1.1 bara) is drawn from the top of the second column 12 and reheated by the heat exchange apparatus (the subcooler 33 and the low-pressure plate heat exchanger 31) for preparation of ultra-low-pressure nitrogen of 1.05 bara (a third nitrogen product).

In some embodiments, waste nitrogen (1.1 bara) is drawn from an upper part of the second column 12 and reheated by the heat exchange apparatus (the subcooler 33 and the low-pressure plate heat exchanger 31) to obtain ultra-low-pressure waste nitrogen of 1.05 bara (a waste nitrogen product).

Embodiment 2

The cryogenic rectification process system is used to prepare high-pressure or ultra-high-pressure air: as shown in FIG. 2, the fifth air stream is guided along the fifth air inlet line 105 with its flow velocity and flow rate controlled by the first regulating valve 1051, and in the air product outlet line 113, is pressurized to a high pressure or ultra-high pressure by the liquid air booster pump 1131, and vaporized via heat exchange through the heat exchange apparatus (the high-pressure plate heat exchanger 32) to obtain the required high-pressure or ultra-high-pressure air product, which is pressurized feed air.

In some embodiments, the flow velocity and flow rate of the third air stream depressurized to the first pressure range are optionally controlled by the first regulating valve 1051, and in the air product outlet line 113, said air stream is pressurized to a high pressure or ultra-high pressure by the liquid air booster pump 1131, and vaporized via heat exchange through the heat exchange apparatus (the high-pressure plate heat exchanger 32) to obtain the required high-pressure or ultra-high-pressure air product, which is pressurized feed air.

In summary, according to the present invention, by adding an air product outlet line and at least one liquid air booster pump to an existing cryogenic rectification process apparatus, the existing rectification apparatus is used to prepare oxygen-enriched liquid air by rectification, and the gas or liquid product produced by rectification can also be used to pressurize and cool the feed air to at least partially liquefy the feed air. Moreover, according to customer requirements, a high-pressure or ultra-high-pressure air product can be discharged by adjusting the ratio of the feed air to the oxygen-enriched liquid air, pressurizing the mixture to a required high pressure or ultra-high pressure by the liquid air booster pump, and then guiding the mixture along the air product outlet line through the heat exchange apparatus for vaporization via heat exchange with the gas or liquid product produced by rectification. According to the present invention, there is no need to provide an additional air compressor or passively increase the discharge pressure of the air booster, so that the production costs are greatly reduced and the energy efficiency level is improved. The method of the present invention can also improve the stability of devices, especially when a small amount of high-pressure/ultra-high-pressure air product needs to be produced. Due to a low flow rate, a piston compressor is required in the traditional method, while the low-temperature liquid air pump used in the present invention is more reliable than the piston compressor.

Although the content of the present invention has been presented in detail by means of the preferred embodiments above, it should be recognized that the description above should not be considered as a limitation to the present invention. Various amendments and substitutions to the present invention will be apparent after perusal of the content above by those skilled in the art. Thus, the scope of protection of the present invention should be defined by the attached claims.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited. 

1-26. (canceled)
 27. A cryogenic rectification process-based method for producing an air product, comprising: a. providing an air separation system for preparing a nitrogen product and/or an oxygen product, which comprises: a rectification column, at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus and at least one heat exchange apparatus, wherein the rectification column comprises a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and the air boost system comprises a main air compressor and at least one air booster; b. after passing feed air sequentially through the main air compressor for pressurization to a first pressure range, the air pre-cooling apparatus for pre-cooling and the air purification apparatus for purification, splitting off one portion thereof as a first air stream for heat exchange through the heat exchange apparatus with a gas or liquid product produced by rectification, and then introducing the first air stream after cooling down into the first column for rectification; and the other portion passing through the air booster for pressurization to a third pressure range before being split into a second air stream and a third air stream, the second air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification and being discharged from a middle part of the heat exchange apparatus into an air expander for depressurization to the first pressure range before being introduced into the first column for rectification; and the third air stream passing through the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, being depressurized to the first pressure range for introduction into the first column or depressurized to a second pressure range for introduction into the second column; c. providing a liquid nitrogen line and an oxygen-enriched liquid air line which introduce liquid nitrogen at the top of the first column and oxygen-enriched liquid air at the bottom of the first column, respectively, into the second column as reflux for rectification; and d. providing an air product outlet line in which at least one liquid air booster pump is arranged, and discharging the oxygen-enriched liquid air or at least partially liquefied feed air of the third air stream from the bottom of the first column through the air product outlet line, into the liquid air booster pump for pressurization to a target pressure, and then into the heat exchange apparatus for vaporization via heat exchange so as to obtain the required air product.
 28. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, wherein the air expander uses an expander booster for braking, the third air stream is first pressurized to a fourth pressure range by the expander booster, then enters the heat exchange apparatus for heat exchange with the gas or liquid product produced by rectification, and after cooling down, is depressurized to a first pressure range by a pressure reducing apparatus and then introduced into the first column.
 29. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, wherein the pressure reducing apparatus is a throttle valve or a liquid expander.
 30. The cryogenic rectification process-based method for producing an air product as claimed in claim 29, wherein the liquid expander is braked by a generator.
 31. The cryogenic rectification process-based method for producing an air product as claimed in claim 28, wherein a fourth air stream is further split off from the third air stream that has been depressurized to the first pressure range, and the fourth air stream is introduced into the second column after being throttled and depressurized to the second pressure range by a throttle valve.
 32. The cryogenic rectification process-based method for producing an air product as claimed in claim 31, wherein a fifth air stream is further split off from the fourth air stream, the fifth air stream is connected to the air product outlet line, and the flow rate and flow velocity of the fifth air stream are controlled via a first regulating valve.
 33. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, wherein the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air.
 34. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, wherein the heat exchange apparatus comprises a low-pressure plate heat exchanger and a high-pressure plate heat exchanger, or an integral combined heat exchanger.
 35. The cryogenic rectification process-based method for producing an air product as claimed in claim 34, wherein the heat exchange apparatus further comprises a subcooler through which the reflux entering the second column exchanges heat with the gas or liquid product rectified by the second column.
 36. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, further comprising: drawing a liquid nitrogen fraction from the first column into the second column as reflux.
 37. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, further comprising: drawing liquid oxygen from the main condensation and evaporation apparatus through a liquid oxygen booster pump for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of the oxygen product.
 38. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, further comprising: drawing the liquid nitrogen from the top of the first column directly into the heat exchange apparatus for vaporization via heat exchange for preparation of a first nitrogen product; or, drawing the liquid nitrogen from the top of the first column through a liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product.
 39. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, further comprising: drawing ultra-low-pressure nitrogen from the top of the second column into the heat exchange apparatus for reheating to prepare a third nitrogen product.
 40. The cryogenic rectification process-based method for producing an air product as claimed in claim 27, further comprising: drawing waste nitrogen from an upper part of the second column into the heat exchange apparatus for reheating to obtain a waste nitrogen product.
 41. An air separation system for producing an air product based on a cryogenic rectification process, the air separation system comprising: a. a rectification column, which comprises: a first column with a first pressure, a second column with a second pressure and a main condensation and evaporation apparatus arranged at the bottom of the second column; and a liquid nitrogen line for guiding liquid nitrogen from the top of the first column through a throttle valve into the second column and an oxygen-enriched liquid air line for guiding oxygen-enriched liquid air from the bottom of the first column through the throttle valve into the second column arranged between the first column and the second column; b. at least one air boost system, at least one air pre-cooling apparatus, at least one air purification apparatus, at least one heat exchange apparatus, at least one air expander, at least one liquid oxygen booster pump, at least one liquid air booster pump and a plurality of pressure reducing apparatuses, the air boost system comprising a main air compressor and at least one air booster; c. a first air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus, the air purification apparatus and the heat exchange apparatus into the first column; a second air inlet line for guiding feed air through the main air compressor, the air pre-cooling apparatus and the air purification apparatus, out of the heat exchange apparatus and then through the air expander into the first column; and a third air inlet line further branching off from the second air inlet line before the second air inlet line enters the heat exchange apparatus, the third air inlet line passing through the heat exchange apparatus directly and being connected to the first column or the second column via the pressure reducing apparatus; d. a liquid oxygen product outlet line for discharging liquid oxygen from the main condensation and evaporation apparatus through the at least one liquid oxygen booster pump and then through the heat exchange apparatus; and e. an air product outlet line connected to the bottom of the first column or the third air inlet line, the air product outlet line being provided with the at least one liquid air booster pump to pressurize at least partially liquefied feed air from the third air inlet line or the oxygen-enriched liquid air discharged from the bottom of the first column to a target pressure for vaporization via heat exchange through the heat exchange apparatus so as to output the required air product.
 42. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 41, wherein the air expander is braked by an expander booster provided, and the third air inlet line is connected via the expander booster and subsequently the heat exchange apparatus and the pressure reducing apparatus to the first column.
 43. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 42, further comprising a fourth air inlet line, which branches off from the third air inlet line connecting the pressure reducing apparatus to the first column and is connected to the second column via the throttle valve.
 44. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 43, wherein a throttle valve or a liquid expander is selected as the pressure reducing apparatus.
 45. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 43, wherein a fifth air inlet line further branches off from the fourth air inlet line, the fifth air inlet line being connected to the air product outlet line for outputting the required air product discharged through the liquid air booster pump and the heat exchange apparatus.
 46. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 45, wherein the fifth air inlet line is further provided with a first regulating valve for controlling the flow rate and flow velocity of an air stream.
 47. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 41, wherein the air product outlet line is further provided with a second regulating valve for controlling the flow rate and flow velocity of the oxygen-enriched liquid air.
 48. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 41, further comprising: a first nitrogen product outlet line for vaporizing the liquid nitrogen from the top of the first column via heat exchange through the heat exchange apparatus for preparation of a first nitrogen product; or, at least one liquid nitrogen booster pump, and a second nitrogen product outlet line passing the liquid nitrogen drawn from the top of the first column through the at least one liquid nitrogen booster pump first for pressurization to a required pressure and then into the heat exchange apparatus for vaporization via heat exchange for preparation of a second nitrogen product; or, a third nitrogen product outlet line discharging nitrogen from the top of the second column through the heat exchange apparatus.
 49. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 41, wherein a liquid nitrogen fraction line for guiding a liquid nitrogen fraction from the first column through the throttle valve into the second column is further arranged between the first column and the second column.
 50. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 49, further comprising a waste nitrogen line for discharging waste nitrogen from the second column through the heat exchange apparatus.
 51. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 41, wherein the heat exchange apparatus comprises a high-pressure plate heat exchanger and a low-pressure plate heat exchanger, or an integral combined heat exchanger.
 52. The air separation system for producing an air product based on a cryogenic rectification process as claimed in claim 51, wherein the heat exchange apparatus further comprises a subcooler for the reflux entering the second column to exchange heat with the gas or liquid product rectified by the second column. 